Two Companies Take Radically Different Approaches to Launcher Reusability

Reaction Engines’ Skylon is a single-stage-to-orbit rocket designed to take payloads into low Earth orbit before returning to the same aircraft-type landing strip from where it took off. Credit: Reaction Engines artist's concept

PARIS — Two companies actively working on reusable launch vehicles on April 11 described their strategies, with one starting in small increments of reusability and the other beginning with a fully formed — if untested — spaceplane.

U.S. and European government officials said they remain believers, if not currently big investors, in the two systems but stressed that the past 20 years of rocket history is littered with designs and flight vehicles — including the U.S. space shuttle — that never met the economic promise of reusable systems.

Dan Dumbacher, NASA deputy associate administrator for exploration systems development, whose background includes work on the shuttle and the NASA-backed X-33 VentureStar spaceplane developed by Lockheed Martin, said reusability presents more engineering and physics challenges than anyone expects.

Dumbacher also stressed the importance of economic considerations. He said the X-33 program, which collapsed following a fuel-tank failure on a test stand, likely would not have survived the changed expectations in the commercial launch market in any event.

The vehicle was developed in the mid-1990s at a time of what proved to be wildly optimistic projections of commercial launch demand.

Addressing the Space Access conference here organized by Astech Paris Region, Dumbacher said the annual flight rate of a reusable rocket, or one that includes major reusable components, is a key to managing the economics.

“The SSMEs were reusable,” Dumbacher said of the space shuttle main engines. “We tried to make them reusable for 55 flights. Look how long and how much money it took for us to do that, and we still weren’t completely successful for all the parts. I want to be realistic: We are not as smart as we think we are and we don’t understand the environment as well as we think we do.”

Christophe Bonnal, a senior expert in the technical division of the French space agency, CNES, recalled an earlier French-Russian joint effort to reuse large strap-on rocket boosters.

“These reusable stages at the start of our studies were just cylinders with engines and little wings,” Bonnal said. “Three years later, they had become complete Airbuses in terms of size, with four engines on each of them. Our main problem was the impact reusability has on the design of the launcher. Safety factors have to be higher, and you need around 30 percent more propellant in the first stage to fly the stage back to the launch site.”

Bonnal said CNES concluded that a reusable first stage could save about 10 percent in costs for a fully expendable rocket if the reusable vehicle flew 50 times per year and the engines could be used nine times on the rocket’s boosters before being used a 10th time as an expendable engine on the rocket’s second stage.

“Then we would save 10 percent — plus or minus 15 percent,” Bonnal said. “We have more to learn.”

Barry Matsumori, SpaceX vice president for commercial sales and business development, said SpaceX is proceeding in small steps by adding legs to the first stage of the company’s currently expendable Falcon 9 rocket to test maneuvering, while continuing parallel testing through the company’s Grasshopper program. Grasshopper will be evolving into the F9R program, aimed at developing a partially reusable variant of the Falcon 9.

Matsumori said it is too soon to estimate how many flights per year would be required of the Falcon 9 with a reusable first stage to generate the savings SpaceX hopes to realize.

SpaceX has told its customers that the company’s Falcon 9 commercial launch prices, already considered low when compared with other launch service providers, should drop further once the first stage is made reusable.

Reaction Engines’ Skylon, meanwhile, is a single-stage-to-orbit rocket designed to take payloads into low Earth orbit before returning to the same aircraft-type landing strip from where it took off.

The company, which labored for years with little government support, has recently received modest backing from the British and European space agencies.

Roger Longstaff, Skylon project manager, said focusing on flight rate is only one way of solving the economics problems around reusable rockets. Reaction Engines, he said, is coming at the market from another angle.

“People ask us: ‘With only 60-70 total launches per year, how can you justify spending admittedly much more than what is needed for an expendable rocket like Ariane 6 — two or three times as much?’” Longstaff said, referring to ESA’s proposed 4 billion-euro ($5.5 billion) future launcher now in design.

Longstaff said Reaction Engines proposes to adapt commercial airline industry practices, where Boeing and Airbus sell plans to multiple airlines that use the same airports.

Under this model, he said, even nations whose governments would launch only once or twice a year might find it valuable to purchase a Skylon and then share spaceport costs.

“It is much easier to buy a spaceplane for somewhere between $500 million and $1 billion than to develop your own system,” Longstaff said. “If you can get sales of around 30 planes, then the business model closes and this can be developed using private funding. If there are fewer, then you are looking at some form of public-private partnership, and this is what we are going to talk to [the European Space Agency] about.”